New dog keeps running off?

i just got this new dog, that some people where giving away and i took him in. we have had him for a week and the first week was great with him, i would let him out and just call him back if he started to wounder off my property. but now he just wants to run away or not listen, Sunday he just took off and my little dog fowled him they went three blocks away with in 5mins. So we decided to hook him up when we let him out now.but today he ran out the door and ran off i had to go chasing after him, i think i know why he is trying to run away, i think he wants to go to his old house like he wants to go home. how can i stop this i'm afraid he will get hit in the road